In this study, an integrated approach for environmental risk assessment of subsurface contamination is proposed. This integration is based on a Monte Carlo method for simulating pollutant transport in subsurface and the consideration of several scenarios for risk assessment guidelines. The method can reflect uncertainties associated with the simulation results and the environmental guidelines, as well as the resulting risks of human health injury. In detail, this research considers:
the fate and transport of the pollutant in heterogeneous porous media under uncertainty c-2, distribution of pollutant concentrations under natural attenuation,
relationships between drinking water standards and health risk guidelines, and
probabilistic quantification of health injury risks.
This method is applied to a site contaminated by leaking underground storage tanks. This results indicate that reasonable outputs have been generated. They are useful for clarifying potential health effects when the groundwater is used for domestic uses, as well as providing support for the related risk-management and remediation decisions.
Pollution problems associated with a number of processes in petroleum industy have generated significant environmental concerns. Among them, leakage, spill, and failure of storage tanks and transport systems often lcad to contamination in subsurface soil and groundwater. They will then cause impacts on public health through oral ingestion, dcrmal contact, inhalation, or food chain exposure pathways. Therefore, the related communities and industries are calling for systematic study on cnvironmcntal risks derived from these contamination problems. The general process of dealing with a pctroleumcontaminated site involves the following steps:
identifying the pollution sources,
simulation of the flow, fate and transport of the pollutants in subsurface,
assessment of the impacts and risks on environment, ecosystem, and public health, and
presentation of the entire process as well as its outputs'. Among these steps, identification of the pollution sources needs to be done by site investigation on all aspects of hydrological and contamination conditions, Uncertainty analysis considers all kinds of uncertain information associated with sampling data, input parameters, and risk assessment process. The simulation module considers numerical prediction of the physical, chemical, and biological behaviors of the pollutant in subsurface.
Previously, studies regarding to subsurface modeling, unccrtainty analysis, and risk assessment have been reported by a large body of literature. In the modeling aspect, Abriola and Pinder proposed a comprehensive approach to simulate simultaneous transport of a chemical contaminant in three physical forms: non-aqueous phase, solute component of a water phase, and mobile fraction of a gas phasel,2. Kaluarachchi and Parker formulated a finite clement model for simulating multi-phase flow of organic contaminants10. Katyal et al. used a two-dimensional finite element program to simulate multi-phase and multi-component transport of contaminants in subsurface with an assumption of the first order decay1, 3. In general, most of the resent modeling efforts were based on multi-phase, multi-component analyses, which can effectively reflect complexities in subsurface systems.